1. Field of the Invention
The present invention relates to a method for generating a write clock of a constant angular velocity optical storage device, and more particularly, to a method that uses a wobble signal to generate a write clock of a constant angular velocity mode optical disk recorder.
2. Description of the Prior Art
For companies or the end users, the management and storage of documents is regarded as an important task. In the past, documents were printed or written on paper. Therefore, when a user deals with a huge amount of documents, it is not convenient for the user to manage those documents because of a great size or a heavy weight. With the development of computer technology, digital data and digital documents are widely stored in a plurality of data storage media. Many kinds of data storage media are developed to help users with those digital data conveniently. An optical disk recorder such as a CD-RW drive takes advantage of recordable compact disks to record data. The compact disk has a low production cost, a small size, and a great storage capacity.
Generally speaking, the optical storage device has two operation modes according to the mode of the motor control. One is a constant linear velocity (CLV) mode, and the other is a constant angular velocity (CAV) mode. With improvements in access speed, constant linear velocity mode is not suitable for a high efficiency or a high resolution application. The reasons are as follows. Under the constant linear velocity mode, the rotational speed of a spindle varies constantly in order to make the associated linear velocity at each position of a disk constant. The rotational speed of the spindle is increased and decreased alternately so that associated power dissipation is raised. The optical storage device, therefore, will suffer a high temperature, a great deal of vibration, and a slow access speed while operating. Therefore, is hard to improve the access speed under the constant linear velocity mode. On the contrary, the rotational speed of the spindle is fixed under the constant angular velocity mode. In other words, the rotation speed of the spindle is fixed, and the associated linear velocity at each position of the disk varies when the optical storage device accesses data from the disk. In addition, when an optical disk recorder under a constant linear velocity mode wants to burn data into the disk, the optical disk recorder cannot record data with a high recording speed because the limitation of keeping a constant linear velocity will prevent the spindle from having a high rotational speed. However, if the constant angular velocity mode is adopted, the spindle operates with a fixed angular velocity so that the outer circle of the disk has a greater linear velocity to improve the corresponding recording speed.
Please refer to FIG. 1, which is a diagram of recording frames according to a prior art disk. The data are first transferred into corresponding eight-to-fourteen modulation (EFM) data when being recorded on a disk. The EFM data are recorded on the disk according to EFM frame format. As shown in FIG. 1A, every 98 EFM frames are combined together to form an absolute time in pre-groove (ATIP) frame. As shown in FIG. 1B, each EFM frame has 588 bits, and the EFM frame comprises synchronization data, subcode data, main data, p-parity data, and q-parity data. The main data, p-parity data, and q-parity data within the 98 EFM frames (ATIP frame) are combined to form a main channel of the corresponding ATIP frame so as to store actual written data. But, the subcode data within every 98 EFM frames are used for storing associated information about the written data such as track numbers. In addition, the subcode data S0 of a first EFM frame F1 and the subcode data S1 of a second EFM frame F2 are used for generating a subcode synchronization signal. The subcode synchronization signal is used for determining synchronization between the EFM data that is prepared to be written and the ATIP data that is pre-recorded on the disk. In addition, when the optical disk recorder transfers the written data into EFM data, the optical disk recorder will simultaneously generate an encoder EFM frame synchronization (EEFS) signal corresponding to each ATIP frame, and an encoded subcode frame synchronization (ESFS) signal corresponding to each EFM frame. The EEFS signal and the ESFS signal are used for determining synchronization status of the written data when the written data are burned into the disk.
Please refer to FIG. 2, which is a diagram of prior art ATIP data 30. When a recordable disk is manufactured, a wobbling track is formed on the surface of the recordable disk. After a pick-up head of the optical disk recorder senses the wobbling track, a wobble signal comprising waveforms with different frequencies is generated. The wobble signal is then decoded according to a frequency modulation (FM) for generating the ATIP data 30 that are related to the recording frames on the recordable disk. The ATIP data 30 are established by blocks. The bit length of each block is equal to 42. The ATIP data 30 has a synchronization mark 31 whose bit length is 4, a data code 32 whose bit length is 24, and a cyclic redundancy check (CRC) code whose bit length is 14. The data code 32 further has minute 34, second 35, and frame 36 information of the recording frame on the recordable disk.
Please refer to FIG. 3, which is a diagram of the prior art ESFS synchronization signal and a prior art ATIP synchronization signal. The synchronization mark 31 of the ATIP data 30 corresponds to an ATIP synchronization signal. According to specification of the optical disk recorder, an error 39 between the ATIP synchronization signal and the ESFS synchronization signal must be controlled within an interval, that is, 2 recording frames of the disk. If the error 39 is greater than 2 recording frames, the recording process fails.
Please refer to FIG. 4, which is a block diagram of a write clock generator 40 according to the prior art CAV optical disk recorder. As mentioned above, the ATIP synchronization signal 41 and the ESFS signal 42 are used to determine whether the recordable disk is ready to record data. Under the CAV mode, the rotational speed of spindle is fixed so that the linear velocity at each position of the disk varies. In other words, the frequency of the wobble signal is unstable due to the frequency variation so that the frequency of the ATIP synchronization signal 41 is affected. In order to make the error between the ATIP synchronization signal 41 and the ESFS signal conform to the limitation defined by the specification, the write clock generator 40 is used for generating a write clock 43 so as to synchronize the ATIP synchronization signal 41 and the ESFS signal 42. A phase detector 44 will generate an output voltage according to a phase difference between the ESFS signal 42 and the ATIP synchronization signal 41. The output voltage is passed through a low-pass filter 46, and is transmitted to a voltage controlled oscillator (VCO) 48. The voltage controlled oscillator 48 then generates a reference clock 50 with a specific frequency according to the output voltage. The reference clock 50 is passed through a frequency divider 52, and a write clock 43 is outputted from the frequency divider 52. Furthermore, the write clock 43 is passed through another frequency divider 54 to alter the frequency of the ESFS signal 42. The above-mentioned process is repeated until the error between the ATIP synchronization signal 41 and the ESFS signal 42 complies with the required specification. That is, when the error between the ATIP synchronization signal 41 and the ESFS signal 42 meets the desired requirement according to the specification, the optical disk recorder can start burning data onto the disk. The write clock 43 is inputted to an EFM encoder 58 so that the EFM encoder 58 can transfer data 56 into a corresponding EFM data signal with the help of the write clock 43. The EFM data signals, which are synchronized with the write clock 43, are then transmitted to a pick-up head 60. Finally, the pick-up head 60 writes data 56 on the disk according to the received EFM data signal.
Based on the ATIP synchronization signal 41, the prior art write clock generator 40 of a CAV compact disk recorder uses a phase-lock loop (PLL) to lock the ESFS signal 42 and the related write clock 43. However, the ATIP synchronization signal 41 has a low frequency. For example, the ATIP synchronization signal 41 has a frequency equal to 75 hertz under “1×” recording speed. Therefore, the phase-lock process requires a long time to compare the phase difference and to adjust the corresponding frequency. That is, the write clock 43 will become stable only after a long period of time, meaning that the recording efficiency and stability of the optical disk recorder are greatly deteriorated.